Recently, there is extensively utilized an endoscope whereby organs within a body cavity can be observed with an elongated insertable part inserted into the body cavity or, as required, various therapeutic treatments can be made by using a treating tool inserted through a treating tool channel.
Various electronic endoscopes wherein such solid state imaging device as a charge coupled device (CCD) is used as an imaging means have been suggested.
Now, in the conventional video camera, the pixel size or the number of longitudinal and lateral pixels (which shall be mentioned as the pixel formation hereinafter) of the imaging device (solid state imaging device) has been of only one kind and no imaging device of two or more kinds has been used. Even in the above mentioned electronic endoscope, the solid state imaging device to be used has been limited to be of one kind.
However, recently, with the development of the endoscope medical science, the observed parts have come to be complicated and manifold and the endoscope tip has come to be required to be finer in the diameter. The allowable outside diameter of the endoscope is different between such thick tube as the large intestine and such thin tube as the bronchus. Therefore, the solid state imaging device of a pixel formation matching a thick tube is too large in the size to form an endoscope for a thin tube. On the contrary, the solid state imaging device matching a thin tube is smaller in the outside diameter than that of the endoscope for a thick tube, therefore produces an excess space, results in wasting the part to be naturally an imaging surface and is not efficient. Therefore, an endoscope having a pixel formation corresponding to the observed part has come to be required.
In an electronic endoscope for observing a body cavity interior by using a solid state imaging device, an electronic zooming function really magnifying the picture image of an affected part has come to be noted as a method of observing the affected part in detail. However, in the conventional electronic endoscope, as the magnification rate of the picture image is fixed, when a solid state imaging device having a different pixel formation is driven, the output picture image will be compressed longitudinally or laterally. In case a solid state imaging device for a small diameter electronic endoscope having a small number of pixels is used, the displaying view angle will be so small that no sufficient observation effect will be obtained. The number of longitudinal scanning lines is 525 in the NTSC system, is 625 in the PAL system and is thus different depending on the television broadcasting. Therefore, in case the solid state imaging device is driven by the same clock, in the
system, as compared with the NTSC system, the size of the longitudinal picture surface will be compressed to be 525/625, the view angle will become smaller and, the same as in the above described example, no sufficient observation effect will be obtained. Therefore, as the clock has been changed in the NTSC system and PAL system, the unit relating to the timing has had to be replaced.
By the way, an example wherein whether a mask is formed or not can be automatically set by discriminating the kind of the endoscope is disclosed in the publication of a Japanese patent application laid open No. 211040/1987. However, even in this prior art example, in case a solid state imaging device having a different pixel formation is used or in case the television broadcasting system is different, the size of the picture image will vary.